I know a lot of you have been waiting for this, and I finally have the time. I'll try to explain this the best I can. Extra special 'thank you' to Flipsen for making outdoor portalling much easier to understand!

For this example we have a hill with 2 players on both sides.


Without outdoor portals the game will draw everything on the other side of the hill for both of them, even though they technically cannot see each other. Why? Because meshes (both terrain & patch) are Detail by default, and Detail brushes do not block vis and/or portals. So here is the solution.

Step 1: When you want to have a portal cell cutting through this terrain, it's best to fill as much unseen area under the terrain with a solid structural brush textured with Caulk. Here is a portal cell without the caulk brush.

This cell goes from the bottom of the skybox to the top, left to right.


This portal cell will work (read: will not fail during compile), but doesn't do much to help FPS. It is correct in the sense that there are no leaks, but because there is nothing to block the view beneath the terrain, everything on the other side of the hill will still be drawn by the game.

Step 2: To block vis on the other side of the hill without actually seeing anything (read: a wall, building, etc...), draw out a caulk brush with the same dimensions as the portal cell that goes from the bottom of the skybox to just under the terrain, and resize the portal cell so it sits right on top of this brush.

As you can see, the caulk brush does not pass through the terrain.


Here it is again with only the caulk brush selected.


Here it is again with only the portal cell selected.


Now there is a Structural brush blocking vis between the 2 players, so as long as your view is below the top of the caulk brush, the game will draw what is going on beyond it, greatly increasing FPS & reducing visible tris. When doing outdoor portals, always use this method when possible, it will help you very, very much, especially with larger maps.

Pt. 2 of this tutorial coming very soon..

Da da da da da, anyone ever need help with portalling let me know!

Nice tut Cornrow!

I get it!